elizabeth roepke 1, josh feinberg 2, david l. fox 2, kena fox-dobbs 1, pratigya polissar 3, katie...
TRANSCRIPT
Neogene to recent paleoprecipitation estimates
in the Meade Basin, Southwest Kansas,
from elemental ratios and rock magnetic
properties in paleosols and modern soils
Elizabeth Roepke1, Josh Feinberg2, David L. Fox2,
Kena Fox-Dobbs1, Pratigya Polissar3, Katie Snell4,
Kevin Uno3, Robert A. Martin5
1Univ of Puget Sound, 2Univ of Minnesota, 3Lamont-Doherty Earth Observatory, 4California Institute of Technology, 5Murray State University
Background & Importance
C4 grasslands 40% of modern terrestrial environments
Ecosystem evolution
Abiotic influence → biotic response• Precipitation, temperature, ash falls
• C3 vs C4 plants
• Small mammal ecology & evolution
Background & Importance
C4 grasslands 40% of modern terrestrial environments
Ecosystem evolution
Abiotic influence → biotic response• Precipitation, temperature, ash falls
• C3 vs C4 plants
• Small mammal ecology & evolution
Ecological impact of precipitation
April 2012 April 2013
Meade Basin
Research Questions
How do grain size, chemical and magnetic
properties vary in 4.5-0 Ma-aged paleosols in the
Meade Basin?
How do paleoprecipitation estimates vary in the
Meade Basin from 4.5-0 Ma?
How do the chemical and magnetic proxies for MAP
compare in these paleosols?
Field Methods
Laboratory Methods
Grain Size:• Remove organics & carbonates• Particles suspended in Na-hexametaphosphate• Laser diffraction
Elemental composition:• Powdered sample digestion in HCl, HF, HNO3
• ICP-OES
Rock magnetic properties:• Percentage of fine grained pedogenic Fe-oxides → frequency
dependence of susceptibility (300 A/m at 465 Hz and 4650 Hz)• Ratio of pedogenic to detrital magnetic oxides → ratio of anhysteretic
to isothermal remanent magnetism (ARM and IRM)
Proxies for MAP
CIA-K (Maynard, 1992; Nordt & Driese, 2010):
C for Mollisols (Sheldon et al., 2009):
Magnetics Proxy (Geiss et al., 2008):
Grain Size Data
10 1000
2
4
6
8
10
Diameter (μm)
Fre
qu
en
cy
(%
)
Elemental Data
0 2 4 6 8 10 12 14
Ca Na Al
Element wt %
Elemental Data
0 2 4 6 8 10 12 14
Ca Na Al
Element wt %
400 600 800 1000
C (mollisols)CIA-K
MAP (mm/yr)
Magnetic Data
3.0 5.0 7.0
ARM/IRM (10-4)
←Huckleberry Ash
Magnetic Data
3.0 5.0 7.0
ARM/IRM (10-4)
400 600 800 1000
MAP (mm/yr)
←Huckleberry Ash
MAP estimates
Further Work
Meade Basin:• Paleosol description/characterization
• Clay mineralogy
• Climate modelling (informed by MAP est.)
Elsewhere:• Magnetic proxy development for non-loessic soils
Acknowledgements
ELT grant #:1338262
References• Geiss C.E., Egli R., & Zanner W, 2008, Direct estimates of pedogenic magnetite as a
tool to reconstruct past climates from buried soils, Journal of Geophysical Research, v. 113, no. B1102. doi: 10.1029/2008JB005669
• Nordt L. C. & Driese S. D., 2010, New weathering index improves paleorainfall estimates from vertisols: Geology, v. 38, no. 5, p. 407–410. doi:10.1130/G30689.1
• Maynard J. B., 1992, Chemistry of modern soils as a guide to interpreting Precambrian paleosols, Journal Of Geology, v. 100, no. 3, p. 279-289.
• Sheldon N. D., Retallack G. J., & Tanaka S., 2002, Geochemical climofunctions from North American soils and application to paleosols across the Eocene-Oligocene boundary in Oregon, The Journal of Geology, v. 110, p. 687-696.
• Fox, D. L., Honey, J. G., Martin, R. A., & Peláez-Campomanes, P. (2012). Pedogenic carbonate stable isotope record of environmental change during the Neogene in the southern Great Plains, southwest Kanses, USA: Carbon isotopes and the evolution of C4-dominated grasslands. Geological Society of America Bulletin, 124(3-4), 444-462. doi: 10.1130/B30401.1
• Fox, D. L., Honey, J. G., Martin, R. A., & Peláez-Campomanes, P. (2012). Pedogenic carbonate stable isotope record of environmental change during the Neogene in the southern Great Plains, southwest Kanses, USA: Oxygen isotopes and the evolution of C4-dominated grasslands. Geological Society of America Bulletin, 124(3-4), 431-443. doi: 10.1130/B30402.1
300 400 500 600 700 800 900 1000
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
CIA-K
C (mollisols)
Magnetics
MAP (mm/yr)
Ap
pro
xim
ate
Ag
e (
Ma
)
MAP estimates• Notes about MAP
trendsModern: 592 ± 147 mm/yr
MAP estimates
Grain Size Data
Discussion• Consistent MAP trends across proxies
• Periods of aridity & humidty
• PC most similar to modern
• PMAG similar prediction as PC• Based on loessic soils